1. Field of the Invention
In one of its aspects, the present invention relates to a radiation sensor device. In another of its aspects, the present invention relates to a fluid treatment system comprising a novel radiation sensor device. In yet another of its aspects, the present invention relates to a radiation sensor module for use in a radiation sensor device.
2. Description of the Prior Art
Optical radiation sensors are known and find widespread use in a number of applications. One of the principal applications of optical radiation sensors is in the field of ultraviolet radiation fluid disinfection systems.
It is known that the irradiation of water with ultraviolet light will disinfect the water by inactivation of microorganisms in the water, provided the irradiance and exposure duration are above a minimum “dose” level (often measured in units of microwatt seconds per square centimeter). Ultraviolet water disinfection units such as those commercially available from Trojan Technologies Inc. under the tradenames Trojan UV Max™, Trojan UV Logic™ and Trojan UV Swift™, employ this principle to disinfect water for human consumption. Generally, water to be disinfected passes through a pressurized stainless steel cylinder which is flooded with ultraviolet radiation. Large scale municipal waste water treatment equipment such as that commercially available from Trojan Technologies Inc. under the trade-names UV3000™, UV3000 Plus™ and UV4000™, employ the same principal to disinfect waste water. Generally, the practical applications of these treatment systems relates to submersion of treatment module or system in an open channel wherein the wastewater is exposed to radiation as it flows past the lamps. For further discussion of fluid disinfection systems employing ultraviolet radiation, see any one of the following:                U.S. Pat. No. 4,482,809,        U.S. Pat. No. 4,872,980,        U.S. Pat. No. 5,006,244,        U.S. Pat. No. 5,418,370,        U.S. Pat. No. 5,539,210, and        U.S. Pat. No. Re 36,896.In recent years, such systems have also been successfully used for other treatment of water—e.g., taste and odour control, TOC (total organic carbon) control and/or ECT (environmental contaminant treatment).        
In many applications, it is desirable to monitor the level of ultraviolet radiation present within the water under treatment. In this way, it is possible to assess, on a continuous or semi-continuous basis, the level of ultraviolet radiation, and thus the overall effectiveness and efficiency of the disinfection process.
It is known in the art to monitor the ultraviolet radiation level by deploying one or more passive sensor devices near the operating lamps in specific locations and orientations which are remote from the operating lamps. These passive sensor devices may be photodiodes, photoresistors or other devices that respond to the impingent of the particular radiation wavelength or range of radiation wavelengths of interest by producing a repeatable signal level (in volts or amperes) on output leads.
Conventional ultraviolet disinfection systems often incorporate arrays of lamps immersed in a fluid to be treated. Such an arrangement poses difficulties for mounting sensors to monitor lamp output. The surrounding structure is usually a pressurized vessel or other construction not well suited for insertion of instrumentation. Simply attaching an ultraviolet radiation sensor to the lamp module can impede flow of fluid and act as attachment point for fouling and/or blockage of the ultraviolet radiation use to treat the water. Additionally, for many practical applications, it is necessary to incorporate a special cleaning system for removal of fouling materials from the sensor to avoid conveyance of misleading information about lamp performance.
International Publication Number WO 01/17906 [Pearcey] teaches a radiation source module wherein at least one radiation source and an optical radiation sensor are disposed within a protective sleeve of the module. This arrangement facilitates cleaning of the sensor since it is conventional to use cleaning systems for the purposes of removing fouling materials from the protective sleeve to allow for optimum dosing of radiation—i.e., a separate cleaning system for the sensor is not required. Further, since the optical radiation sensor is disposed within an existing element (the protective sleeve) of the radiation source module, incorporation of the sensor in the module does not result in any additional hydraulic head loss and/or does not create a “catch” for fouling materials.
Conventional radiation sensor devices typically have been designed as field units with the detector (e.g., photodiodes, photoresistors and the like) being calibrated prior to assembly into the sensor body. The sensor body is then sealed in a conventional manner to prevent ingress of fluid.
Recently, the United States Environmental Protection Agency (“USEPA”) published guidelines for ultraviolet radiation sensor devices for use in municipal drinking water treatment systems. These published guidelines prescribe the use of one sensor per radiation source in municipal drinking water treatment water systems. The published guidelines also prescribe: the use of one or more filters to limit the sensitivity of the detector (e.g., photodiodes, photoresistors and the like) to the germicidal range, limitations on accuracy/tracability of the sensor device, requirements for regular sensor recalibration and a requirement that UV intensity sensors should view a point along the length of the lamp that is between the electrodes (lamp end) and within 25% of the arc length away from the electrode.
The incorporation of a filter into a sensor device can create a degree of uncertainty if it is not possible to calibrate the specific detector (e.g., photodiodes, photoresistors and the like) paired with the specific filter. If the specific detector is calibrated alone before being paired with the specific filter in the final application, small variations in the composition of the filter and/or position of the filter could impact the sensitivity of the detector and reduce the accuracy of the sensor when compared to an absolute irradiance or radiation dose.
In conventional ultraviolet radiation sensor devices, it is not possible to physically adjust the calibration set point of the detector without first completely dissembling the sensor device.
Accordingly, there remains a need in the art for a sensor device ideally suited to match a specific sensor to a specific radiation source in a 1:1 ratio and to allow for ready removal of the sensor device, verification of calibration of the detector (e.g., photodiodes, photoresistor and the like) and adjustment thereof as required.